Supplementary Material for: First karyotypic insights into Potamotrygon schroederi Fernández-Yépez, 1958: association of different classes of repetitive DNA

Introdution
Currently, there are 38 valid species of freshwater stingrays, and these belong to the subfamily Potamotrygoninae. However, cytogenetic information about this group is limited, with studies mainly using classical techniques, Giemsa and C-banding.
Methods
In this study, we used classical and molecular cytogenetic techniques (mapping of repetitive sequences 18S, 5S and SSRs) in order to investigate the karyotypic composition of P. schroederi and draw a parallel with the karyoevolutionary trends of this group.
Results
The species presented 2n=66 chromosomes with 18m+12sm+16st+20a, heterochromatic blocks distributed in the centromeric regions of all chromosomes, and terminal blocks in the q arm of pairs 2 and 3. Mapping of 18S rDNA regions revealed multiple markers on pairs 2 and 7 and a homolog of pair 24. The 5S region was found in the pericentromeric portion of the subtelocentric pair 16. Furthermore, dinucleotide SSRs sequences were found in the centromeric and terminal regions of different chromosomal pairs, with preferential accumulation in pair 17. In addition, we identified conspicuous blocks of (GATA)n and (GACA)n sequences colocalized with the 5S region (pair 16).
Conclusion
In general, this study corroborates the general trend of a reduction in 2n in the species of this subfamily. Also, we finding that the location of rDNA regions is very similar in Potamotrygon. Besides, the microsatellite acumulation in the second subtelocentric pair (17) seems to be a common trait amog Potamotrygon species.

引言
目前已确认的淡水魟有效物种共计38种，全部隶属于河魟亚科（Potamotrygoninae）。然而该类群的细胞遗传学资料仍较为有限，现有研究多采用经典细胞遗传学技术，即吉姆萨（Giemsa）染色法与C带显带技术。
研究方法
本研究结合经典与分子细胞遗传学技术（对18S、5S核糖体DNA及简单序列重复序列（SSRs）进行定位），对施罗德河魟（P. schroederi）的核型组成展开分析，并与该类群的核型进化趋势进行对比。
研究结果
该物种的染色体数目为2n=66，核型组成为18条中着丝粒染色体（m）+12条亚中着丝粒染色体（sm）+16条亚端着丝粒染色体（st）+20条端着丝粒染色体（a）；异染色质块分布于所有染色体的着丝粒区域，且在第2、3对染色体的长臂（q臂）存在末端异染色质块。18S rDNA区域定位结果显示，其在第2、7对染色体及第24对染色体的同源染色体上存在多个标记位点。5S rDNA区域定位于第16对亚端着丝粒染色体的着丝粒旁区域。此外，二核苷酸简单序列重复（SSRs）序列分布于不同染色体对的着丝粒与末端区域，且在第17对染色体上呈现优先富集现象。同时，本研究还发现(GATA)n与(GACA)n序列的显著富集区域与5S rDNA区域（第16对染色体）发生共定位。
结论
总体而言，本研究证实了河魟亚科物种的染色体数目（2n）存在减少的整体进化趋势。同时，本研究发现河魟属（Potamotrygon）物种的核糖体DNA区域位置具有高度相似性。此外，微卫星序列在第17对亚端着丝粒染色体上的富集现象，似乎是河魟属物种的共有特征。